1. Field of the Invention
This invention relates generally to Transformer Turns Ratio Testing and more particularly to test fixtures for increasing the speed of Transformer Turns Ratio Testing.
2. Description of the Prior Art
During a useful life of 25 to 40 years a utility network distribution transformer, for example, is subjected to a variety of tests on many occasions starting with acceptance tests upon delivery, to verify name plate and other data. One of the tests of interest to utility companies is determination of the Transformer Turns Ratio (TTR). One type of transformer turns ratiometer uses a standard reference transformer which has accurately calibrated tappings used with a hand cranked exciting magneto, current and voltage meters for normalizing the flux level and a null indicator which indicates the exact transformer turns ratio to 0.1%.
Another method of TTR measurement involves connection of the transformer primary and secondary windings in series with additive polarity. A means is provided for excitation of the windings with a standard current. A potentiometer across the series connected windings with the movable arm connected to the primary and secondary junction through an AC null indicator permits determination of the ratio of primary to secondary turns.
A delta-star connected, three phase utility transformer has three primary terminals and four secondary terminals. Measurement of the ratio of three pairs of primary and secondary windings involves connection of four leads of the ratiometer to each of the six windings in turn and with correct polarity.
The Biddle TT (Transformer Turn) Ratiometer is a four terminal testing device. The four inputs are extended to six feet with flexible instrument leads. Connection to the transformer primary is through a pair of insulated leads terminating in spring loaded clips. Each secondary connection is via an instrument lead which is a dual conductor consisting of a current wire and a potential or voltage wire. The Biddle potential/current leads are connected to the transformer lugs being measured with a specially designed "C" clamp. The stationary end of the "C" clamp is insulated from the clamp body and terminates in an insulated pressure pad which is connected to the potential lead. The frame of the "C" clamp is connected to the secondary current lead. The potential and current leads are connected to the Biddle Ratiometer, thus the connections to each transformer secondary lug is made at a point on each side of the terminal lug which may be anywhere from 1/2".times.1/2" to 3/4".times.4", depending on the KVA (Kilo-Volt-Ampere) rating of the transformer.
The need to connect and disconnect, for example, the Biddle TT ratiometer primary leads and to clamp and unclamp the secondary connectors three times to perform turns ratio measurements on a common core three phase transformer or on three single phase transformers connected in a delta-star configuration, indicated that a need existed for a device which would permit the three required turns ratio measurements to be made quickly and without the need for making separate connections to the seven transformer terminals.